Currently, more than half the adults in the U.S. are considered to be overweight, and almost one quarter of these adults meet or surpass the criteria for obesity (BMI>30 kg/m2). Numerous studies of related and unrelated individuals have provided support for the role of genes in the determination of body size and mass. This is particularly true in the case of morbidly obese young adults, in whom a genetic susceptibility for obesity very likely precedes or exacerbates the effects of overeating or lack of physical activity often found in these individuals. Prevention programs designed to reduce the risk of obesity commonly focus on modifiable environments and behaviors such as physical activity and diet, with varied results among individuals. This heterogeneity in response to obesity interventions is also at least in part of genetic origin. Nevertheless, little is known about how genetic variation in genes related to the regulation of body mass/fat and obesity may alter or influence one's response to exercise or diet intervention. Though the number of genetic factors that may be related to obesity is substantial, at least four mechanisms may contribute to an individual's body composition response to exercise intervention: 1) predisposition for the formation and growth of adipose tissue, 2) propensity for muscle cell growth or maintenance, 3) sensitivity to factors that influence satiety, and/or 4) alterations in energy metabolism. Thus, the purpose of this study is to investigate the association between genetic variation within genes related to adipogenesis, myocyte differentiation and growth, satiety, and energy metabolism and response to a well-established 30-week exercise training protocol, as determined by changes in body composition and blood lipids, in a multi-racial cohort of college-age men and women. In addition, we will investigate levels of gene expression in adipose and muscle tissue samples both pre- and post-training in order to identify additional genes related to body composition and/or responsivity to exercise. We have selected a powerful sample of males and females from multiple racial groups (N=1,536) designed to maximize our likelihood of detecting genetic differences related to body composition change. Results of this study will be invaluable not only in understanding the processes of exercise response and body composition change but also in improving intervention programs designed to reduce or prevent obesity.